The understanding of the molecular basis of Epstein-Barr virus (EBV)entry into target cells and virion trafficking in infected cells is the long-term goal of the Lonanecker Laboratory. We anticipate that discoveries related to EBV entry and virion morphogenesis in infected cells will be important for the development of therapeutics to treat EBV-associated cancers in the human host. Our overall hypothesis that drives our research focus is that EBV gB interacts with specific cell surface receptors that facilitate viral fusion and entry into EBV target cells. In addition, the cytoplasmic tail of EBV gB interacts with host and viral proteins and this interaction is important for regulating fusion, but also required for proper egress of EBV capsids from infected cells. The tissue tropism for EBV in vivo is largely limited to cells of epithelial or lymphoid origin. The cellular and viral factors required for EBV entry of target B cells has been fairly well described. The major viral envelope glycoprotein 350/220 (gp350/220) binds to CR2/CD21 that is abundantly expressed on B cells. Subsequently, gp42 binds to HLA Class II triggering fusion mediated by gB and gH/gL. Few details are known in regard to the mechanism of EBV induced membrane fusion and viral entry into epithelial cells. It is apparent that other receptors function in epithelial cells since CD21 and HLA Class II are not typically expressed on epithelial cells. Lindsey Hutt-Fletcher has provided compelling evidence to suggest that EBV entry of epithelial cells when compared to B cells is mechanistically different. In our preliminary studies, we have shown that in contrast to B cells, which require gp42, gB, and gH/gL for efficient cell fusion, epithelial cells require only gB, and gH/gL and when a mutant form of gB is used, only gB is required for efficient cell fusion indicating that gB may be the major fusion protein for epithelial cells and that a specific epithelial receptor for gB may exist. This proposal will analyze: 1 - The role of gB in EBV entry of epithelial and B cells by the identification of important gB functional domains by site-specific and random mutation. 2 - The role of the gB cytoplasmic tail in regulating fusion and mediating virion morphogenesis as well as the function of several cellular proteins that bind the gB tail will be determined. 3 - The existence of a novel gB receptor will be investigated. Clarifying the interactions between EBV and target cells is essential for understanding the tropism of EBV infections in the human host. Knowledge of the mechanism and viral and cellular factors required for EBV entry and replication in epithelial and B cells will provide insight into host susceptibility and will allow for the development of therapeutics for the treatment or eradication of EBV-associated diseases.